This grant is to support a broad program of epidemiologic studies to elucidate the etiology of cancer and identify means of prevention. Emphasis is on studies of the role of estrogen metabolism in the etiology of breast cancer, on factors responsible for international differences in survival of breast cancer patients, on the risk of cancer among users of oral contraceptives, on the possibility that coffee drinking is associated with bladder cancer, on the possibility that Hodgkin's disease is trasmitted by contact from case-to-case or via intermediaries, on the risk of leukemia amoung patients treated with radiotherapy for malignant disease and on descriptive, hypothesis- seeking studies of cancers of the pancreas, ovary and central nervous system and multiple myeloma. Supporting the eqidemiologic work are proposals for experimental studies of carcinogenesis in rats and for development of statistical methodology for epidemiologic studies.